McALLEN, Texas (AP) — The Biden administration’s plan to build new barriers along the U.S.-Mexico border in South Texas calls for a “movable” design that frustrates both environmentalists and advocates of stronger border enforcement.

The plans for the nearly 20 miles (32 kilometers) of new barrier in Starr County were made public in September when the federal government sought public input. The following month, the administration waived 26 federal laws protecting the environment and certain species to speed up the construction process.

“The United States Border Patrol did not ask for this downgraded border wall,” Rodney Scott, a former U.S. Border Patrol chief said.

Construction is moving forward despite President Joe Biden’s campaign promise not to build more wall and amid an increase in migrants coming to the nation’s southern border from across Latin America and other parts of the world to seek asylum. Illegal crossings topped 2 million for the second year in a row for the government’s budget year that ended Sept. 30.

People such as Scott who want more border security believe the barriers won’t be strong enough to stop people from crossing illegally. Environmentalists, meanwhile, say the design actually poses a greater risk to animal habitat than former President Donald Trump’s border wall.

Biden has defended the administration’s decision by saying he had to use the Trump-era funding for it. The law requires the funding for the new barriers to be used as approved and for the construction to be completed in 2023.

Most barriers on the border were erected in the last 20 years under Trump and former President George W. Bush. Those sections of border wall include Normandy-style fencing that resembles big X’s and bollard-style fencing made of upright steel posts.

Biden’s barrier will be much shorter than the 18- to 30- foot (5.5 to 9-meter) concrete-filled steel bollard panels of Trump’s wall. It also could be temporary.

An example of the style of barrier his administration will use can be seen in Brownsville, about 100 miles (161 kilometers) southeast of Starr County. Metal bollards embedded into 4-foot-high (1.2-meter-high) cement blocks that taper toward the top sit along the southern part of a neighborhood not far from the curving Rio Grande.

Over the last year, the Rio Grande Valley region was the fourth-busiest area for the number of people crossing into the U.S. illegally, though it was the busiest in previous years.

With the design planned for Starr County, federal border agents will be able to move around the fencing, said Democratic U.S. Rep. Henry Cuellar, who represents Starr County. “So it’s one of those things where if they want to direct traffic, they can move it.”

Scott agreed that the “moveable” fences can be used as an emergency stopgap measure to block off access in some areas. But he warned that if the fencing isn’t placed far enough into the ground, someone might be able to use a vehicle to shove it out of the way, provided they don’t mind damaging the vehicle.

Laiken Jordahl, a conservation advocate with the Center for Biological Diversity, said mountain lions, bobcats, javelinas, coyotes, white-tail deer, armadillos, jack rabbits, ground squirrels, and two endangered, federally protected plants — Zapata bladderpod and prostrate milkweed — may be affected.

Jordahl said the design the Biden administration is using “will block even the smallest species of animals from passing through the barrier.”

“The one advantage for making it shorter is, I guess if somebody falls while they’re climbing over it, they aren’t falling as far,” Scott Nicol, a board member of the Friends of the Wildlife Corridor, said.

Nicol, who lives in the Rio Grande Valley, is familiar with the type of barriers Biden’s administration will use, the terrain, and the weather in Starr County. He is concerned about unintended consequences, particularly on the Rio Grande that separates U.S. and Mexico.

“You know, if Starr County gets hit by a big rainstorm and the water has to drain into the river, these walls — whether it’s the bollard walls or the Jersey barrier walls — are going to block the movement of that water and dam it up,” Nicol said.

Last month, the Center for Biological Diversity along with about 100 other organizations sent the U.S. government a letter pleading for reconsideration of environmental protection laws. To date, they have not received an answer.